The IPL is incompatible with the GPL because it contains restrictions not included in the GPL. According to the FSF “it requires certain patent licenses be given that the GPL does not require. (We don’t think those patent license requirements are inherently a bad idea, but nonetheless they are incompatible with the GNU GPL.)”

OpenSMTPd is very nice, I’m using it in a few places with simpler, less mission-critical sendmail|postfix setups. If you’re familiar with PF’s syntax, the smtpd syntax will be familiar. It is more about rules then about lists of variables that affect behaviour. The fact that SMTP AUTH+TLS is built-in, both in sending and receiving is a bonus (AFAIR postfix still requires patches for that).

That the smtpd grammar (in yacc. like the rest of the OpenBSD daemons’) converted to SVG by GraphViz::Parse::Yacc fits completely on my screen is a win.

billthk: Exim’s license is GPL, which is unacceptable for new code going into the OpenBSD base system, so it wasn’t considered (it is available as a port).

I’ve always found courier-mta to be rather straight forward. Easier than sendmail / exim, for sure. More versatile than qmail too. GPL3 licensed. But I’m definitely not against the idea of an even better SMTPD.

Nothing wrong with sendmail. Exim is a horridly-written replacement of it: The syntax in the config files are really irregular and the default Debian setup concatinates a bunch of files together so that the errors show up in completely unrelated locations.

Postfix is a nice simple MTA, but I found that when I tried it last (about 5 years ago) it just didn’t have the features for header rewriting, mail routing, spam filtering, and such for even a medium-sized mail hub for 100 people with a variety of servers feeding it mail.

Sendmail on the other hand combines the elegance of both of these. A sendmail config file is rarely more than 5 or 6 lines long until some new feature is needed. At that point, you have access to databases to store information, a language that allows really fine tuned manipulation of email flows and rewrites, and debugging tools that allow you to see the flow of email from beginning to end.

And the really lovely part? Sendmail has had *all* of this since the early 90’s when I started using it. It holds up well under ridiculous load, has a response upstream and all of the other lovely goodness.

I’ve never heard a complaint about Sendmail that didn’t come from someone who’d actually used a version that didn’t come with SunOS (or from someone who’d never used it at all and points to things that aren’t the human-usable config files)